Michael S. Tsirkin wrote:
Add module option hw_csum: when set, IPoIB will report S/G
support, and rely on hardware end-to-end transport checksum (ICRC)
instead of software-level protocol checksums.
Since this will not inter-operate with older IPoIB modules,
this option is off by default.
Hi Michael,
looking on slide 18 of Dror's Sonoma presentation (*) which states -
Checksum Offload
TCP/UDP/IP Checksum Offloading - Query device for checksum offload support
QP Creation - Mark QP for IPoIB checksum support
TX - ibv_send_flags indicate checksum offload request
RX - ibv_wc_flags indicate checksum status (good, bad, unverified)
I don't see that there is such dependency, nor I can understand the
design that creates the dependency, unless you rely on the IB CRC and
not compute the actual TCP/UDP/IP csum.
Can you clarify the exact limitation that prevents inter-operation? why
does the receiving side side cares if the checksum at the sender was
computed by the SW or the HW (and vise versa)?
I know some people find this approach controversial,
but from my perspective, this is not worse than e.g.
SDP which does not have SW checksums pretty much by design.
Is this b/c of the non interoperability?
SDP is not inter-operate by design where IP/TCP stack over IPoIB MUST
support interoperability. Not inter-operable TCP checksum offload is not
very useful, I think.
Or.
(*) see
http://openfabrics.org/archives/spring2007sonoma/Tuesday%20May%201/gdror%20Next%20Generation%20Hardware%20Assists%20And%20Scalability2.pdf
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